Adaptations and selection of harmful and other dinoflagellate species in upwelling systems 1. Morphology and adaptive polymorphism

The complex three-dimensional physical structure, spatial scale and the variations in the upwelling-relaxation cycles characterizing eastern boundary upwelling systems are summarized. It is suggested that upwelling systems and their bloom dynamics should be accorded the status of biomes. A unique upwelling dinoflagellate flora is not found. The harmful, red tide and other dinoflagellates selected to bloom are cosmopolitan in distribution and commonly bloom in coastal habitats. The morphological features of 27 dinoflagellate species that bloom in upwelling systems are compared to identify commonalities in form and function adaptations relevant to their upwelling occurrences. The upwelling dinoflagellate species are morphologically, physiologically, ecologically and toxicologically diverse; a unique set of morphological traits specifically evolved for growth in upwelling systems is not evident. The absence of a unique dinoflagellate upwelling flora is unexpected given the challenges to survival and growth in upwelling systems posed by the energetic physical conditions and spatial and temporal complexity of upwelling dynamics. Cellular defense mechanisms - armouring and small cell formation - against external and internal cellular damage resulting from turbulence-induced stress-strain, and the occurrence of morphological streamlining to facilitate swimming-based strategies adaptive to growth in upwelling systems are evaluated. The occurrence of autotomy, ecdysis, thecal resorption and regeneration, seasonal cyclomorphosis and polymorphism (form variation) among dinoflagellates is evaluated. The impressive commonality and rapidity of ecomorph formation suggest autoregulated polymorphism is potentially an important mode of adaptation available to upwelling dinoflagellates, and specifically directed towards adjustment of their flotation (swim:sink ratio) capacity. However, seasonal cyclomorphosis and regional and local displays of adaptive polymorphism are traits shared with dinoflagellates generally, rather than unique, or specific to the upwelling dinoflagellates. It would appear that the morphological traits, including the requirements of hydrodynamic streamlining and shear tolerance, evolved to accommodate the swim-based ecology of the dinoflagellates, as distinguished from the sinking strategy of diatoms, allow dinoflagellates to exploit the complex niche structure of upwelling systems without the need for special adaptations. The greater conundrum is what are the mechanisms that select for upwelling dinoflagellate species and their blooms, and not their adaptations. Published by Elsevier Ltd.